Hello Rich -- welcome to MobileRead.
Since you are starting a store selling eBooks, I'd love to give you some input. First and foremost, PDF is only suitable for printing or maybe for reading on a full-sized screen. It is *NOT* suitable for reading on a hand-held reader unless the PDF is explicitly produced for the small screen. (Note also that there are devices that don't support PDF files.) I own both a Kindle and a Sony reader, so I'm usually looking for "multi-format" eBooks so that I only have to buy the book one time, but I can get it in both formats. That allows me to decide which reader I'm going to use when I get ready to read the book, not weeks or months ahead of time when I'm buying it.
If you want to see an online eBook store that gets it right, check out Baen's Webscription site at
http://www.webscription.net/
We're glad you've dropped in at MobileRead. And, since you'll be selling eBooks, it might be a good idea for you to pick up at least one device so you can have hands-on experience to help you better understand your customers.